Glitch Trainer with Pokémon over level 100 of any species, sometimes even ?????. The game may also suddenly display "Waiting..." as if it was in a link battle. Once this message is displayed, the game will freeze.

RAM physically damaged

Glitch Trainer with numbers in their name, usually with Pokémon over level 100

Sometimes during a link battle—possibly due to a dusty, damaged, or loose link cable—one of the players can send invalid data to the other player. This triggers a corrupted link battle with a different result for each player. Usually the opponent withdraws the Pokémon which was fighting to send out a glitch Pokémon that wasn't in their party. The players will battle against an AI using mostly the Pokémon which were in the party of the opponent but also glitch Pokémon usually over level 100 and asleep. In particular, many corrupted link battles trigger a Butterfree with a large amount of HP, making it actually undefeatable and forcing the player to restart the game. If a player had an Egg in their party, then the Egg can be sent out by the AI and appear with the sprite and the moves of the Pokémon which is inside the Egg, but it will immediately faint.

A corrupted link battle has a good chance to corrupt the Trainer House and the mailbox of the player who received the invalid data, while it won't affect the player who sent the invalid data. The glitch Trainer obtained in this way can be battled, but the screen may display "Waiting...!" as if the player was in a link battle. Once the message "Waiting...!" is displayed, the game will freeze. A corrupted link battle can be forced by having a Pokémon with an irregular HP bar.

It is also possible to obtain the Trainer House glitch if the last Mystery Gift was corrupted by an infrared interference. In this case, the item received will be unaffected, but the Trainer House could be corrupted.

Time method

This method usually occurs if the player sets the time back just after a trade or a Mystery Gift. The Trainer in the Trainer House is replaced with PKMN TRAINER Thomas. PKMN TRAINER Thomas is displayed in the receptionist's dialog as a series of "9" and letters. This PKMN TRAINER is displayed in battle with six Pokémon, which are all fainted, and sends out a level 0 ????? with his same sprite causing an immediate freeze. PKMN TRAINER Thomas doesn't corrupt the player's mailbox, and can be fixed by doing a new Mystery Gift or a trade, which should replace the missing information.

Unown method

A glitch Mystery Gift policeman may appear on the second floor of any Pokémon Center, and will give the player a random item

A Pokémon over level 100 of the glitch Trainer

This glitch overwrites data associated with the mailbox and Trainer House with a certain index number depending on the hexadecimal identifier of a viewed glitch Unown in the Unown Dex, causing alterations to the game. If the new value triggers a glitch Unown then the time will be reset and the Trainer in the Trainer House will be displayed without a valid name, but with six Pokémon. Battling the Trainer twice (or even once) in one day often either freezes the game or triggers the glitch dimension. The glitch Trainer may have Pokémon with glitch status conditions and Pokémon over level 100, and may have Pokémon with impossible movesets and Pokémon with a series of "?" instead of their name. Some glitch Pokémon know a glitch move which, if used, causes the message "But nothing happened" to appear, followed by the game entering the glitch dimension. Additionally, if the player checks Unown's Pokédex data in a Pokémon Center or inside a city, there will be a Policeman on the second floor of all Pokémon Centers, as if the player had received a Mystery Gift. When spoken to, he says "Hello ! You're <player>, right? I have something for you." If the player chooses "YES", the Policeman will say "Here you go!" and the player will receive an item (this item is related to the glitch Unown index number). This allows the player to obtain various glitch items, such as the Teru-sama.

Trainers

Registering glitch Unown

To register a glitch Unown in the Unown Dex, the player may obtain a ????? (Hex FF) as a bad clone from the Celebi Egg glitch. If the ????? is placed as the first Pokémon in the party, the player can use the "MOVE PKMN W/O MAIL" option to withdraw over 6 Pokémon. This corrupts RAM data located past the expected end of the Pokémon data structure, although there are only a limited amount of Pokémon that the player can withdraw before the game freezes. If details about a 'post-6' Pokémon conflicts with data about Pokémon in the Unown Dex, then it is possible to replace entries with glitch Unown, provided that the player already has the Unown Dex, for example the index number of the current fourth move's PP of Pokémon #11 conflicts with RAM data associated with the first Unown. It is possible to replace the first Unown with a glitch Unown this way provided that the player used PP Ups to raise its associated index number past 26. In the process of obtaining glitch Unown, the player will be corrupting the values of other RAM addresses such as those determining seen or owned Pokémon in the Pokédex, or the number of options on the menu.

If the player added a glitch Unown which activates a glitch dimension, then there is a possibility that it will trigger the Trainer House glitch depending on its index number. Since getting a glitch dimension from glitch Unown only partially saves the game, any values changed prior such as the number of Pokémon seen and owned in the Pokédex will be returned to normal, provided that the player did not already save from the menu. A list of glitch Unown which give obtainable Mystery Gift items can be found below.

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List of obtainable 'Mystery Gift' items

Below are a list of Mystery Gift items obtainable through glitch Unown, based on the viewed hexadecimal identifier.
Some hexadecimal values can trigger two or more items depending on where the glitch Unown is displayed. Missing hexadecimal values don't trigger any item.

Related problems

A mailbox corrupted by this glitch. The messages may be signed from unused character strings

It is rare that the Trainer House data is corrupted without simultaneous corruption of other areas of the save.

A glitch message in a corrupted mailbox. It's signed by GREEN

Most commonly, the player's mailbox is corrupted. If so, the list is not properly terminated. Some of the messages may be signed from unused character strings, such as GREEN (a default character name remnant from the Japanese version), and some may freeze the game or reset it into a glitch dimension if they are read. If the player gives one of these messages to a Pokémon, and the mail appears as a purple version of the Flower Mail from the mailbox, the game will transform it into an equivalent item depending on its index number. All invalid Mail will appear this way, except for index number 255, which causes the screen to become blank.

If the player has an excessive number of glitch messages the overworld will become corrupted, the screen may turn black and the NPC sprites will become corrupted sprites. If the player has around 230 messages the game will freeze or reset into a glitch dimension.

By reading or scrolling past these messages, a series of side-effects may occur:

Wild Pokémon and Trainers not inside the Trainer House may become glitchy. In this case, the Trainers will have the same name and Pokémon as the last Trainer fought in a link battle. If the player hasn't performed a link battle, their first Pokémon will be a Wigglytuff. The screen will display "Waiting..." when the player attempts to fight as if they were in a link battle.